1. Technical Field
This invention relates to a power supply apparatus and, more specifically, to a power supply apparatus for preventing a pole change or reversal of a plurality of power cells configured electrically independently, while continuing their reasonable operation, and for performing a reasonable operation conforming to a load power.
2. Background Art
FIG. 7 is a block diagram showing a fuel cell apparatus according to a conventional technology (Patent Document 1). As shown in this drawing, the fuel cell apparatus is designed to supply electric power, which has been generated in a fuel cell stack 100, to a load 109 via a power converter 103 for regulating the electric power to be a predetermined output voltage (desired voltage) designated by a controller 108.
The fuel cell stack 100 has a plurality of unit cells 110 connected in series, and each of the unit cells 110 is supplied with a fuel and air via a fuel supply device 101 and an air supply device 102. The controller 108 sets the amount of fuel supply and the amount of air supply for each unit cell 110 based on the respective voltages of the plurality of unit cells 110 measured by a voltage measuring instrument 105, allows the fuel to be supplied to each unit cell 110 via the fuel supply device 101 based on the amount of fuel supply for each unit cell 110, and allows air to be supplied to each unit cell 110 via the air supply device 102 based on the amount of air supply for each unit cell 110. The purpose of this procedure is to minimize variations in the respective voltages of the plurality of unit cells 110.
In this manner, the amount of fuel supply is increased or decreased for each unit cell 110 to stabilize the electric power generated, thereby preventing declines in the voltages of the unit cells 110 and the deterioration of each unit cell 110, due to variations in the characteristics of each unit cell 110 or variations in the supply of fuel. That is, variations in the voltages of the unit cells 110 are curtailed in an attempt to stabilize the electric power generated by the fuel cell stack 100.    Patent Document 1: JP-A-2006-73379    Patent Document 2: JP-A-2004-303621
The above-described fuel cell apparatus according to the conventional technology is designed to curtail variations in the voltages of the unit cells 110, thereby stabilizing the electric power generated by the fuel cell stack 100. However, the fuel cell apparatus cannot detect an abnormal drop in a voltage generated by each unit cell 110. If the unit cell 110 with such an abnormally dropped voltage continues to be used, the unit cell 110 undergoes reversal and becomes unusable.
To prevent reversal, a technology, which comprises detecting a voltage generated in each power generation cell and isolating an abnormal power generation cell from the stack, has been proposed (Patent Document 2). With this technology, however, there is the problem that once a power generation cell has generated an abnormal voltage, this power generation cell is continuously isolated, making a reasonable operation impossible. That is, with the technology disclosed in Patent Document 2, once the generated voltage has fallen, the isolated state is continued even when power generation capacity recovers later. However, even after an abnormal drop in the generated power for a cause, such as fuel insufficiency, temporary stoppage or halt of power supply often results in the subsequent recovery of power generation capacity. In such a case, it is not necessary to continue the isolated state of the power generation cell.
The fuel cell apparatus shown in FIG. 7 mentioned above, on the other hand, has the fuel supply device 101 for each unit cell 110. Thus, it also has problems, such that 1) the structure of the fuel cell apparatus is complicated, 2) the fuel cell apparatus is upsized, and 3) the weight of the fuel cell apparatus is increased.
Even upon control for increasing or decreasing fuel supply, there may be a case where a drop in the voltage of each unit cell 110 cannot be prevented (for example, the fuel supply path is clogged, or the cell is short-circuited (physically or chemically)). In this case, the effect of stabilizing the generated power due to control for increasing or decreasing fuel supply is not obtained, causing the problem of wasteful fuel supply and fuel consumption.
The present invention has been accomplished in the light of the above-described conventional technologies. It is an object of the invention to provide a fuel cell apparatus which can detect an abnormal voltage drop in a power generation cell and, if its power generation capacity is recovered, resume power generation; and can select a cell necessary for power generation in accordance with a load power, thereby realizing reasonable and stable power supply to the load with long-term power generation reliability.